DIGESTION OF PCR PRODUCTS

Dear colleagues,
I am trying to introduce restriction sites at the 5' and 3' end of PCR
products, to ligate the digested product in a vector. Until now I've
been unsuccesfull in doing so. At the 5' end I've introduced a KpnI site
with 6 bp in front of it; at the 3' end I've introduced a BglII site with
2 bp extra at the 3' end (should be sufficient according to the New England
Catalog).
After PCR, I treat the products with Proteinase K to remove Taq polymerase
sticking to the ends, and digest the product with the restriction enzymes
and ligate it into a vector digested with KpnI and BglII.
Unfortunately, the transformed ligation product doesn't yield any colonies.
Can someone help me solve this problem?
Thanks very much in advance,
Marcel Kuiper.